1. Field of the Invention
This invention relates to a suspension control system for an automotive vehicle, which properly controls a suspension performance by detecting the road surface condition in front of the vehicle.
2. Description of the Related Art
Conventional devices for detecting the condition of a road surface in front of a vehicle include an optical type as disclosed in Unexamined Japanese Patent Publication No. 60-142208 (U.S. Pat. No. 4,781,465; GB 2151872; DE 3447015; FR 2557288) and an ultrasonic type as disclosed in Unexamined Japanese Patent Publication No. 62-131813. These publications suggest that the suspension performance can be properly controlled in accordance with the detected road surface condition in front of the vehicle.
While the former of the above two prior art publications does not give a specific example of suspension control, the latter discloses a technique of controlling the damping coefficient of a shock absorber in accordance with the detected condition of the road surface in front of the vehicle.
In the above control system, the damping coefficient is changed to a smaller value when the forward road surface is detected to be rough, to thereby effectively prevent an impulsive high vibration from being induced by a projection on the road surface or a junction of pavement when wheels run over it.
If, however, the damping coefficient is controlled to be a smaller value even when the forward road surface is extremely rough and thus a particularly high vibration is input to the vehicle, the suspension is likely to undergo a bottoming out. If the suspension undergoes such a bottoming out, a strong and impulsive high vibration is transferred to the vehicle body and the ride feeling is spoiled.
The object of this invention is to provide a suspension control system for an automotive vehicle in which the detection of the road surface condition in front of the vehicle is effective so that the ride feeling is improved when the vehicle travels on a moderately rough road. Further, a bottoming out of the suspension is prevented, which could have occurred when the vehicle ran on an extremely rough road.